Support OGRs network and compressed file access methods.

I.e. file names starting with /vsicurl/ and/or /vsizip/, /vsigzip/
and /vsitar/.
Handle .gz .tar.gz and .zip files transparently.
Add options --idfile and --saveid to read and write starting and ending ID from files.
Update tests for --idfile and --saveid options.
Make elementIdCounter a class variable in Geometry.

Simplify getNewID().
Make globals features and geometries class variables.
Move class definitions to a separate file, geom.py.

This is to make them accessible to translation functions.